1. Field of the Invention
The present invention relates to a groove machining method for forming thin bottomed grooves in the surface of a metal workpiece using a laser and a honeycomb structure forming die using the same method and a method for producing the same die.
2. Description of the Related Art
Conventionally, machining using a laser has been used for welding and cutting a workpiece, but there has been no case where the laser machining is used for machining grooves having bottoms or bottomed grooves. In a cutting method using laser, a laser beam is emitted onto the workpiece to melt it, and a melted portion is removed with an assist gas or high-pressure water. To be specific, a laser beam is emitted onto the workpiece in such a manner as to be converged to a single location thereon so as to form a through hole, and then the laser beam emitting location is shifted to form another through hole in the workpiece. Thus, the workpiece is cut by continuously forming through holes.
In a case where an attempt is made to use this method to form grooves, it is possible to form through grooves which have no bottoms, but bottomed grooves have not been formed using the method. In addition, in the method in which the melted portion is removed by jetting high-pressure water, water remains on the surface of the workpiece, causing a problem that the path along which the laser beam is emitted is altered owing to the water so remaining on the surface of the workpiece, whereby the laser beam cannot be emitted onto a desired position with accuracy.
On the other hand, grid-like grooves are formed in a honeycomb structure forming die from which a ceramic honeycomb form is extruded. Most of these grooves are bottomed grooves which are large in depth and small in width. While grinding or electrical discharge machining has been used a method for forming such grid-like grooves, as there is an increasing tendency that the widths of grooves are required to be narrower to such as 100 xcexcm or smaller, it is becoming more difficult to employ the aforesaid grinding and electrical discharge machining in which a grinding wheel and electrodes are physically used, respectively.
Incidentally, for example, a ceramic honeycomb structure made from mainly cordierite is produced by extruding the material using a forming die. This honeycomb structure so formed is constituted by many cells which are formed by providing bulkheads in a grid-like fashion, and in many cases the cells are each formed into, for example, a quadrilateral or hexagonal shape.
In addition, the aforesaid honeycomb structure forming die is used as a honeycomb structure forming die having supply holes for supplying a material and grooves adapted to communicate with the supply holes, respectively, for forming the material supplied from the supply holes into the aforesaid honeycomb shape.
In recent years, there has been a demand that the thickness of bulkheads of the honeycomb structure is smaller and is, for example, 100 xcexcm or smaller. To cope with this demand, naturally, the width of the grooves of the honeycomb structure forming die must also be smaller.
However, if the width of the grooves of the honeycomb structure forming die is made narrower, as required, the flowability of the material which is supplied from the supply holes and then passes through the grooves is deteriorated. This increases the forming pressure while forming is carried out, leading to a risk that formability is reduced.
The invention was made in view of the problems inherent in the prior art, and an object thereof is to provide a method for forming narrow and deep bottomed grooves using laser, and a honeycomb structure forming die for forming a thin honeycomb structure without reducing the formability by making use of the bottomed grooves forming method and a method for producing the same forming die.
According to an aspect of the invention, there is provided a laser groove machining method for forming bottomed grooves in the surface of a workpiece using laser, wherein an emitting position of laser which is to be emitted on the workpiece is shifted relatively along groove forming positions at a high speed of 150 mm/min. or faster.
According to this groove machining method of the invention, the relative shifting speed of the laser beam emitting position is made to be the aforesaid high speed of 150 mm/min. or faster, whereby melted portions resulting at the surface of the workpiece, through the emission of the laser beam, can be blown off along the grooves so formed with an assist gas, thereby making it possible to separate, cool and remove the melted portions. Namely, the melted portions can be separated, cooled and removed with ease without forming through holes. This allows the laser machining, which has conventionally been used only for cutting and welding, to be applied to machining bottomed grooves.
According to another aspect of the invention, there is provided a method for producing a honeycomb structure forming die having supply holes for supplying a material and grooves adapted to communicate with the supply holes and formed into a grid-like configuration for forming the material into a honeycomb configuration, each groove having a groove depth which is ten times or more as large as a groove width thereof, wherein in machining the grooves in a die material, an emitting position of a laser beam, which is to be emitted to a surface of the forming die material which is opposite to a surface thereof where the grooves are formed, is shifted along groove forming positions.
According to this honeycomb structure forming die producing method of the invention, the method is adopted in which the laser beam is shifted relatively in machining the grooves, whereby grooves whose depth is greater than the width can be produced with ease.
Namely, in a case where grooves are formed in the die material, only by a laser beam, melted portions formed through being subjected to the emission of the laser beam set as they are, making it difficult to form grooves. Here, according to the method of the invention, as is described above, the laser beam is shifted relatively, whereby the melted portions can be separated, cooled and removed with easy by separating, cooling to set, and removing the melted portions with an assist gas. Thus, narrow and deep grooves can be formed using a laser with ease.
According to a further aspect of the invention, there is provided a honeycomb structure forming die having at least supply holes for supplying a material and grooves adapted to communicate with the supply holes and constructed to form the material into a honeycomb configuration, wherein inclined portions are provided at corner portions formed where bottom portions of the grooves intersect with sides of the supply holes, and wherein, at the inclined portions, the depth of the grooves gets deeper as the grooves approach the supply holes.
According to the honeycomb structure forming die of the invention, as is described above, the depth of the grooves is not uniform but is constructed to be deeper as the grooves approach the supply holes by providing the inclined portions at the corner portions. Owing to this, the material is allowed to flow smoothly when it passes from the supply holes to the grooves.
Namely, as the corner portions where the bottom portions of the grooves intersect with the sides of the supply holes are inclined, the material, which passes from the supply holes to the grooves, expands gradually along the inclined portions. Owing to this, when compared to a case where there is provided no inclined portion at the corner portions, the change in flowing direction when the material expands in the width direction can be reduced. Because of this, the material is allowed to flow smoothly when it penetrates into the grooves from the supply holes.
Then, owing to this, even in case the width of the grooves is made narrower, an increase in forming pressure can be suppressed, thereby making it possible to maintain a superior formability.
According to another aspect of the invention, there is provided a method for producing a honeycomb structure forming die having at least supply holes for supplying a material and grooves adapted to communicate with the supply holes and constructed to form the material into a honeycomb configuration, comprising the steps of forming the supply holes from a hole forming surface of a die material, thereafter jetting water to groove forming positions on a groove forming surface opposite to the hole forming surface so as to form a pillar of water so that a laser beam is emitted through the interior of the pillar of water and implementing scanning of the emitted laser beam in which the laser beam emitting position is shifted along the groove forming positions in such a manner as to pass along the same groove forming positions a plurality of times, increasing the number of times of scanning the emitted laser beam in the vicinity of corner portions formed where bottom portions of the grooves intersect with sides of the supply holes and forming inclined portions at the corner portions so that the depth of the grooves gets deeper as the grooves approach the supply holes.
According to this aspect of the invention, as described above, the laser beam which is caused to pass through the pillar of water is used to machine the grooves. In addition, the depth of the grooves is made to get deeper gradually by implementing the emission scanning of the laser beam as described above.
Thus, the depth of the grooves can be changed locally by changing the number of times of implementation of the emission scanning locally by adopting the laser machining method that has just been described above.
Owing to this, according to the aspect of the invention, the number of implementations of the emission scanning is increased in the vicinity of the corner portions formed where the bottom portions of the grooves intersect with the sides of the supply holes by changing the number of implementation of the emission scanning, whereby the inclined portions are formed at the corner portions so that the depths of the grooves become deeper as the grooves approach the supply holes.
In addition, according to the aspect of the invention, the laser beam is emitted through the pillar of water as described above, whereby the laser beam advances while being confined within the diameter of the pillar of water, so that the width of the grooves can be controlled to fall within the diameter of the pillar of water with accuracy. Owing to this, the groove machining that can well meet the accuracy required for the honeycomb structure forming die can be implemented with ease.
Thus, according to an aspect of the invention, the aggressive adoption of the aforesaid laser machining method enables the realization of the local change in depth of the grooves, which has been extremely difficult to be realized by the conventional grinding or electrical discharge machining. In addition, in particular, the honeycomb structure forming die which can provide the smooth flow of the material can be obtained by changing the depth of the grooves in such a manner as to form the inclined portions at the corner portions.
The present invention may be more fully understood from the description of preferred embodiments of the invention set forth below, together with the accompanying drawings.